In a switched network environment, such as a telephone system, packet-switched data network, or asynchronous transfer mode (ATM) network, it is useful to be able to "tap" into calls in progress. In today's telephone networks, tapping is used primarily for surveillance purposes in compliance with state or federal regulations. In a data network, however, there is another compelling use for a "tap" facility: the diagnosis of protocol problems between different systems on the network. This has traditionally been done by applying a "probe" or "analyzer" to one of the links across which the conversation is occurring and filtering the data to expose the conversation of interest. The problem with this approach is that the "probe" as well as the expert who is interpreting the data, must be located at a tappable point on the correct link. This requires the movement of equipment and personnel and is time consuming, expensive and impractical in many situations. It also requires special "tap-points" to be available on the link or disruption of the link to insert the probe.
Many modern packet and cell-switches provide the capability of programming multipoint connections, i.e., connections for which data, when received by the switch, is sent out more than one port. These are used, for example, to create point-to-multipoint connections, such as described in the ATM-Forum UNI (User-Network-Interface) Specification. A point-to-multipoint connection has a single data source, but multiple receivers of the data.
It would be desirable to provide a tapping function that was not limited to special "tap-points" on the network and which did not require the insertion of special equipment at a designated location. Ideally, it would be desirable to have the ability to monitor any conversation occurring on the network at any one of a number of different locations, without requiring the insertion of a probe or the presence of an expert technician at a specified location.
It is an object of the present invention to provide a ubiquitous call tapping facility in a switched network which utilizes the network's own multipoint connection services.